De-icing or anti-icing apparatus



United States Patent DE-ICING'OR ANTI-ICING APPARATUS Alexander GordonFarries, Luton, England, assignor to DrNapier & Son Limited, London,England, a British company Application January 27, 1955, Serial No.484,466

Claims priority, application Great Britain January 29, 1954 7 Claims.(Cl. 219-19) This invention relates to thermoelectric surface heatingapparatus, such as for example de-icing or anti-icing apparatusfor thesurface parts of aircraft and the like, which may be exposed. to icingconditions, and of the kind including a thin layer of conductingmaterial which forms a resistance heating element, and is usuallysandwiched between two electrical insulating layers. Examples of suchapparatus are describedin the specifications of United States copendingapplications Ser. No. 304,964 and Ser. No. 392,228 in which theconducting material is in the form of a sprayed metal. layer and theinsulating layers consist of thermo-settingplastic'material each appliedin an uncured state and subsequently cured.

In such apparatus the conductingmaterial is usually in the form ofsprayed aluminium or an aluminium alloy in view of its readyavailability, ready application by spraying and general suitability forthe purpose in question.

In any case, in order to provide the required-length of conducting pathin a convenient manner and yet cover the required area of surface theconducting layer is in many casesin the form of a pattern which includesa sereis of relatively wide heater strips either inclined to one anotheror parallel to one another and separated by narrow gaps and connected attheir ends by transverse strips of approximately the same width as theheater strips, so as to form a zig-zag or other non-liner electricalpath with the heater strips electrically in series with one another.With this arrangement, it is found that there is a concentration ofcurrent and therefore of heat dissipation in the inside of the bends,that is to say, in the case of parallel strips, in the parts of eachtransverse strip adjacent to the adjacent edges of the heater strips,while the outer parts of the transverse strips and/or the adjacent outeredges of the heater strips remain comparatively unheated.

It is an object of the present invention to provide an arrangement inwhich such heat concentrations and comparatively cold areas will beavoided and more even heating over the whole of the required area thusobtained.

To this end according to the present invention electrical surfaceheating apparatus of the kind comprising a thin layer of conductingmaterial constituting a heater element, formed in a patterncomprising atleast two heater strips having ends lying adjacent to one another, andconnected together electrically in series, includes it connectingconductor element between the adjacent ends of the heater strips, theconnecting element being narrower than the two heater strips which itconnects and having a lower electrical resistance per unit of lengththan the heater strips, and contacting the ends of the heater stripsover substantially their full widths.

it will thus beseen that each connecting element constitutes inetfect abus bar by which the electric current flow is distributed oversubstantially the whole width of the-end of each of theheater stripswhich it connects.

. Preferably the connecting element is formed at least ice partly of amaterial having a higher efiective electrical conductivity than that ofthe heater strips. Moreover the connecting element is preferably soformed thatthe heating efliect per unit surface area of the connectingelement is substantially the same as the heating effect per unit area ofeach of the heater strips.

Conveniently the thickness of the connecting element is greater thanthat of the heater strips. The width of the connecting element may vary,but it is preferably less than one third, and may be less than onequarter of the width of the heater strips.

In a preferred construction the main heater strips are formed ofaluminum while the connecting element is formed at least partly ofcopper or silver, and the metal may be applied by spraying.

Conveniently however the connecting element comprises an underlayer ofthe same thickness and material as the heater strips, and a subsidiaryupper layer applied over the underlayer.

in one form of the invention the two heater strips are parallel to oneanother, and the connecting element is arranged transversely across twoadjacent ends of the strips.

In another form the two heater strips are arranged at an angle to oneanother, with the end of one strip abutting the side of. the otherstrip, and the connecting element is of cranked formation including twoparts in con tact with the ends of the two heater strips.

The invention may be performed in various different ways but somespecific embodiments will now be described by way 'of example withreference to the accompanying drawings in which:

Figure l is a fragmentary plan view of a bend in an electrical heaterelement according to a prior proposal,

Figure 2 is a corresponding view of part of a heater element accordingto the present invention,

Figure 3 is a'somewhat diagrammatic perspective View of the elementshown in Figure 2.

Figure 4 is an enlarged diagrammatic sectional view on the line IV-IV inFigure 2 in which the relative dimensions have been distorted for thesake of clarity, and

Figures 5 and 6 are plan views of modifications of the invention.

in the previous construction illustrated in Figure l the adjacent endsof 'two parallel heater strips 1 and 2 are connected by a transversestrip 3 which is of the same thickness and width and formed of the samematerial as the strips 1 and 2. The resulting current distributionaround the bend has been determined by experiment and as shown in Figure1 it results in a tendency to overheat at the inside 4 of the bend andthe formation of cold spots at the outer corners 5 of the bend, This isparticularly disadvantageous in surface heaters applied to aircraftsurfaces for de-icing purposes, since the hot spots may causedeterioration of the structure, while the cold spots may result in theaccumulation of ice.

in the example of the invention illustrated in Figures 2, 3 and 4 thetwo parallel strips 1 and 2 are connected by a transverse connectingelement 6 which has a lower effective resistance per unit of length inthe direction of current flow and is of relatively smaller width w, andextends across the full widths W of the ends of the strips 1 and 2. Theresulting current distribution is illustrated in Figure 2 and it will beseen that this construction tends to reduce the tendency to theformation of cold spots at the outer corners of the bends. V

The formation of the transverse strip 6 is preferably such that theheating effect and therefore the surface tenr perature of this strip isapproximately equal to that of the strips 1 and 2. The total currentpassed through the transverse strip 6. is the same as that passed byeach of the strips 1 and 2 and the heating effect per unit surface areaof this strip therefore depends upon the specific resistance of thematerial, and its width and thickness. By appropriate choice of each ofthese factors the heating effect may be made to correspond to that ofthe main strips 1 and 2.

In one particular example the main parallel heater strips 1 and 2 areeach 0.5 inch wide and of the order of thousandths of an inch thick andare designed to give heat dissipation at the rate of watts per squareinch when passing a current of 10 amps. The resistance of these mainheater strips is thus .05 ohm per inch length. In such case thetransverse strip 6 is conveniently .125 inch wide, and since its rate ofheat dissipation is to be the same at 10 watts per square inch surfacearea, the resistance per inch of length of this transverse strip must bein the neighbourhood of .0125 ohm. In any case, in order to obtain therequired results, the width of the connecting element is preferably lessthan one third, or one quarter, of the width of the associated heaterstrips.

The transverse strip 6 may be a separate element applied to the surfaceand abutting the ends of the strips 1 and 2. Alternatively the mainheater element including the parallel heater strips 1 and 2 may beformed with a narrow transverse strip of the same dimensions in plan asthe transverse strip 6, and the connecting element may then be built upby the addition of one or more further layers of conducting material 7as shown in Figures 3 and 4. This construction is particularlyconvenient where the main heater strips 1 and 2 are applied in the formof sprayed metal, for example sprayed aluminum, in which case the upperlayer of the transverse strip 6 may also be applied by spraying and maybe in the form of copper or silver or other high conductivity metal.

As mentioned above the invention is particularly applicable toelectrical surface heating equipment for use as de-icing or anti-icingequipment on the exposed surfaces of aircraft and similar bodies. Insuch case the apparatus is preferably built up in the form illustratedin Figure 4. The metallic aircraft skin 8 is first covered by a layer ofa synthetic thermosetting plastic adhesive 9 having good electricalinsulating qualities. This plastic is preferably applied to the aircraftskin by a spraying process. The main electrical heater element strips 1and 2 are then applied also by a hot spraying process through a stencilto give the required pattern, and the top transverse element 7 isapplied in the form of sprayed copper on top of the end portions ofthese strips. A further layer 19 of the same synthetic plastic resin isapplied over all and the whole structure is then heated to a temperaturewhich will effectively cure the synthetic plastic.

It will be understood that the invention is not confined to connectionsbetween parallel heater strips but may also be used in any case wherethe current path is caused to flow round a bend. For example in Figure5, a right angled bend is illustrated, and in this case the connectingelement 12 between a pair of heater strips 13 and 14 is of L shape inplan, and contacts the ends of both strips, one of which abuts the sideof the other. In Figure 6 is illustrated a 45 bend.

It will be seen that the invention enables a uniform temperature to bemaintained within fine limits over substantially the whole of thesurface to be heated.

It will be apparent also that, since both the heater strips and theconnecting elements are applied preferably by metal spraying, theapparatus can be produced with approximately the same ease and hassubstantially all the advantages as regards appliability by readilyavailable equipment to surfaces of compound curvature, and ease ofrepair if damaged, of the apparatus forming the subject of United Statescopending applications Ser. No. 304,964 and Ser. No. 39,228.

What I claim as my invention and desire to secure by Letters Patent is:

1. Electrical surface heating apparatus for an exposed aircraft surfaceand of the kind comprising a thin layer of conducting materialconstituting a heater element on said surface, formed in a patterncomprising at least two heater strips having ends lying adjacent to oneanother, and connected together electrically in series, and includingheat-emitting connecting conductor element between the adjacent ends ofthe heater strips, the connecting element being narrower than the twoheater strips which it connects and formed at least partly of a materialhaving a higher effective electrical conductivity than that of theheater strips such that the heating effect per unit surface area of theconnecting element is substantially the same as the heating effect perunit area of each of the heater strips, said connecting elementcontacting the ends of the heater strips over substantially their fullwidths and said connecting element avoiding cold spots by providingsubstantial temperature uniformity in the connect ing element.

2. Electrical surface heating apparatus for an exposed aircraft surfaceand of the kind comprising a thin layer of conducting materialconstituting a heater element on said surface, formed in a patterncomprising at least two heater strips having ends lying adjacent to oneanother, and connected together electrically in series, and including aheat-emitting connecting conductor element between the adjacent ends ofthe heater strips, the connecting element being narrower than the twoheater strips which it connects and having a thickness greater than thatof the heater strips such that the heating effect per unit surface areaof the connecting element is substantially the same as the heatingeffect per unit area of each of the heater strips, said connectingelement contacting the ends of the heater strips over substantiallytheir full widths and said connecting element avoiding cold spots byproviding substantial temperature uniformity in the connecting element.

3. Electrical surface heating apparatus for an exposed aircraft surfaceand of the kind comprising a thin layer of conducting materialconstituting a heater element on said surface, formed in a patterncomprising at least two heater strips having ends lying adjacent to oneanother, and connected together electrically in series, and including aheat-emitting connecting conductor element between the adjacent ends ofthe heater strips, the connecting element being narrower than the twoheater strips which it connects and having a lower electrical resistanceper unit of length than the heater strips such that the heating effectper unit surface area of the connecting element is substantially thesame as the heating effect per unit area of each of the heater strips,said connecting element contacting the ends of the heater strips oversubstantially their full widths, said connecting element avoiding coldspots by providing temperature uniformity in the connecting element andthe main heater strips being formed of aluminium while the connectingelement is formed at least partly of a material selected from the groupcomprising copper and silver.

4. Electrical surface heating apparatus for an exposed aircraft surfaceand of the kind comprising a thin layer of conducting materialconstituting a heater element on said surface, formed in a patterncomprising at least two heater strips having ends lying adjacent to oneanother, and connected together electrically in series, and including aheat-emitting connecting conductor element between the adjacent ends ofthe heater strips, the connecting element being narrower than the twoheater strips which it connects and having a lower electrical resistanceper unit of length than the heater strips such that the heating effectper unit surface area of the connecting element is substantially thesame as the heating effect per unit area of each of the heater strips,said connecting element contacting the ends of the heater strips oversubstantially their full widths, said connecting element avoiding coldspots by providing temperature uniformity in the connecting element andthe connecting element comprising an under- 5 layer of the samethickness and material as the heater strips, and a subsidiary upperlayer applied over the underlayer.

5. Electrical surface heating apparatus as claimed in claim 1 in whichthe two heater strips are parallel to one another, and the connectingelement is arranged transversely across two adjacent ends of the strips.

6. Electrical surface heating apparatus as claimed in claim 1 in whichthe two heater strips are arranged at an angle to one another, with theend of one strip abutting the side of the other strip but electricallyinsulated therefrom, and the connecting element is of angled formationincluding two parts in contact with the ends of the two heater strips.

7. Electrical surface heating apparatus according to claim 2 in whichthe two heater strips are parallel to one References Cited in the fileof this patent UNITED STATES PATENTS 1,172,025 Homan Feb. 15, 19161,996,522 Norris Apr. 2, 1935 2,527,720 Guyer Oct. 31, 1950 2,622,178Glynn Dec. 16, 1952 2,622,828 Lucas et al. Dec. 23, 1952 2,627,012Kinsella et a1 Jan. 27, 1953 2,641,675 Hannahs June 9, 1953 2,648,754Lytle Aug. 11, 1953 2,665,090 Holdaway et a1 Jan. 5, 1954

